Summary

I updated my (MSI GP72) laptop running Kubuntu 18.04 to 18.10, using sudo do-release-upgrade. The upgrade completed successfully and the system was restarted.

Now the GUI doesn't show up.

You hear the sound of the greeter coming up, but the login screen is never displayed; you only see a black screen.

I can login using the terminals and use the laptop "normally", both locally or remotely (I can SSH into it), but the GUI is never shown.

I've seen other questions with similar symptoms, but their issues had clearly visible error messages and/or log entries that helped identify the problem (e.g. reinstalling a driver, etc) and have not been helpful for me.

How can I fix this issue?

Some Troubleshooting

Other than my notes below, I've not found any (obvious) error messages; I've checked the following log files:

/var/log/syslog: shows some nvidia errors (verbose; see later)

/var/log/boot.log

/var/log/kern.log

/var/log/dpkg.log

/var/log/nvidia-installer.log

/var/log/gpu-manager.log: shows the nouveau driver not loaded and blacklisted

/var/log/Xorg.0.log: only a line with No monitor specified for screen "nvidia". stands out to me

While it could be that the files are being found elsewhere (dkms and lsmod show the drivers loaded), the odd part is that it also complains about not being able to execute /usr/bin/nvidia-smi, yet the file exists and I can run it just fine from the shell.